Lateral-Facet Elevating Trochleoplasty
Simon Donell
Iain McNamara
INTRODUCTION
Pathogenesis
Trochlear dysplasia is a known risk factor for patellar instability.
Lateral elevation trochleoplasty was first described by Albee in 1919.1 He described an elevating osteotomy of the lateral facet of the trochlea to deepen the trochlear groove for recurrent patellar dislocation when the groove was flat.
Recent studies have shown that in five out of six cases of trochlear dysplasia, the pathology is located in the center and/or medial trochlea. Only in 17%, the pathology is caused by lateral trochlea/lateral femoral condyle (LFC) hypoplasia.2
LFC hypoplasia is a form of trochlear dysplasia where the lateral facet of trochlea is flat, hypoplastic, or less inclined than normal.
It is now recognized that lateral-facet elevation trochleoplasty is indicated only in the presence of LFC hypoplasia and flat trochlea.
Elevating the lateral facet of the trochlea in the presence of trochlear hyperplasia (and in the absence of LFC hypoplasia) increases the patellofemoral joint reaction force and increases the risk of subsequent patellofemoral osteoarthritis.
Recently, it has been recognized that the LFC hypoplasia may affect different parts of the LFC/lateral trochlear facet—proximal, anterior, distal, and global. The Albee procedure is ideally suited for anterior LFC hypoplasia.
The pathogenesis of LFC hypoplasia is presumed to be a failure of physeal growth.
The presentation is a lateral patellar dislocation, typically occurring from internal rotation of the femur with the foot planted on the floor and minimal trauma.
Proximal LFC hypoplasia leads to patellar dislocation in knee extension and distal LFC hypoplasia in flexion. Global LFC hypoplasia results in the risk of a lateral patellar dislocation occurring in any degree of knee flexion.
Classification
LFC hypoplasia can be divided into four anatomic variants (Figure 20.1):
Anterior—absence of lateral condylar edge/flare/inclination
Distal—short, flattened trochlea/femoral condyle in distal-lateral aspect
Proximal—short trochlea in its proximal-lateral extent (see Chapter 21)
Global—combination of all the above
EVALUATION
Patient History
The patient should describe obvious episodes of lateral patellar dislocation, but spontaneous reduction is typical because there is no lateral edge to the trochlea. The patella may also be permanently dislocated.
The precise functional problems need to be elucidated, and the expectations of treatment recorded.
The position of the knee during the dislocation episodes may indicate where the hypoplasia exists.
A family history of dislocation as well as hypermobility syndromes, including generalized joint laxity, should be noted.
Details of the rehabilitation program and supervision following a dislocation should be noted to check that this has been optimal. An operation is indicated when conservative therapy has failed.
Physical Examination and Findings
Physical examination should include the following:
The patient’s body mass index because obesity affects muscle function and requires a motivated patient to rehabilitate adequately.
The Beighton score to exclude generalized joint laxity and hypermobility syndromes.
The overall lower limb alignment, especially a valgus knee and hip version with tibial torsion.
Figure 20.1 A, Normal perfect lateral radiograph with overlapping of posterior condyles. B, The trochlear line (black dotted line) is flush with the anterior femoral cortex. The condylar line (white dotted line) demonstrates the anterior flare of the trochlear facets. Trochlear dysplasia as a result of lateral condylar hypoplasia could affect the proximal part (P), anterior aspect (A), or distal aspect (D) of the lateral femoral condyle/lateral trochlear facet.
The presence and power of the vastus medialis obliquus muscle.
The presence of an effusion suggesting intra-articular chondral damage or a loose body, although a loose body is less likely when there is no groove to capture the patella.
Patellar apprehension.
The shape of the trochlea: This can be palpated when the knee is fully flexed and will be flat, with the lateral rim absent.
The type of patellar tracking: Global and distal LFC hypoplasias are more likely to result in dislocation in flexion.
The range of knee movements and the extensor and flexor power.
Hip muscle function and proprioception by asking the patient to stand on each leg to test balance and single-leg squat to test gluteus maximus muscle function. A step-down test will do the same where there is an adductor moment found on the knee with femoral internal rotation. The gluteus maximus muscle externally rotates the femur and so is essential to keep the patella tracking straight.
Table 20.1 lists indications and contraindications for lateral-facet elevating trochleoplasty.
TABLE 20.1 Indications and Contraindications for Lateral-Facet Elevating Trochleoplasty | ||||
|---|---|---|---|---|
|
Imaging
Routine imaging for assessing any patient with recurrent lateral patellar dislocation should be undertaken including:
Plain radiographs with a strict lateral view where the posterior femoral condyles match precisely (Figure 20.1).
Standing long-leg alignment views if there is a significant valgus clinically.
Magnetic resonance imaging (MRI) scan to assess trochlear and patellar shape.
Computed tomography (CT) to assess overall lower limb rotational alignment if a significant abnormality has been noted on physical examination.
In the majority of patients with trochlear dysplasia, the trochlea is hyperplastic (ie, decreased trochlear depth), so a recession trochleoplasty should be performed along with any associated procedures necessary to stabilize the extensor mechanism. hyperplasia can be assessed from the MRI scan by the anteroposterior trochlear measurements, as proposed by Biedert and Bachmann2 (Figure 20.2).
The heights of the lateral (L) and medial (M) condyles and the trochlea (T) are recorded as a
percentage of the width of the femur (W) on axial MRI. The values for normal, hyperplastics (decreased trochlear depth), and hypoplastic LFC are shown in Table 20.2. The figures for LFC hypoplasia have not been reported but are predicted as showing the lateral condyle being the same height as the trochlear height.
Figure 20.2 Measurement of the lateral condylar height. The lateral condylar height (L) is expressed as a percentage of the width of the femur (W). The same is done for the trochlear height (T) and medial condylar height (M). Trochlear dysplasia could be as a result of trochlear hyperplasia (red dotted line) or lateral condylar hypoplasia (blue dotted line). Reprinted from Biedert RM, Bachmann M. Anterior-posterior trochlear measurements of normal and dysplastic trochlea by axial magnetic resonance imaging. Knee Surg Sports Traumatol Arthrosc. 2009;17:1225-1230 with permission from Springer.
Normally, LFC hypoplasia is noted from the lateral plain radiograph. This shows absence of lateral condylar flare. The trochlear groove line lies flush to the anterior distal femoral cortex (Figure 20.3); the boss height is, therefore, 0 mm (Dejour grade B).
In addition to the plain radiographs, MRI scan gives further information about the articular cartilage. It is now recognized that the hypoplasia can also be distal3,4 and, if not identified, is a cause of failure of an isolated medial patellofemoral ligament reconstruction.
TABLE 20.2 Anteroposterior Trochlear Measurements (As Percentage of Femoral Width) of Normal and Dysplastic Trochlea by Axial Magnetic Resonance Imaging
Type of Trochlea
Lateral (%)
Trochlea (%)
Medial (%)
Normal
81
73
76
Hyperplastic (decreased trochlear depth)
82
77
79
Hypoplastic lateral femoral condyle
73a
73a
73a
a Theoretical values.
The LFC may not extend proximally enough to capture the patella during the early stages of knee flexion, resulting in proximal dysplasia and a short trochlea (Figure 20.1). The MRI scan can indicate the length using the technique suggested by Biedert et al5 (see Chapter 21).Related posts:
Surgical Considerations During Patellar Stabilization
Quadricepsplasty Techniques for Patellar Stabilization
Lateral Retinacular Release and Lengthening
Chondral Lesions and Patellar Instability
Proximal Femur Rotational Osteotomy
Failed Medial Patellofemoral Ligament Reconstruction: Causes and Treatment
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